1. Field of the Invention
The present invention relates to power supplies for image intensifiers wherein two or more image intensifiers are coupled to a single power supply of the type in which changes in total intensifier power relative to intensifier input illumination are sensed by a current detector to provide a negative feedback signal for controlling the intensifier input voltage, to regulate the operating voltages applied to the intensifier which in turn regulates the image intensifier output light intensity. The present invention also relates to multiple image intensifier systems as aforedescribed wherein the high light saturation level and low light gain response of the image intensifiers are independently adjustable. The foregoing are advantageously incorporated into night-vision goggle systems.
2. Description of the Prior Art
Image intensifier tubes of the prior art have widely varying characteristics, among which are overall gain at low light levels and high light level saturation characteristics. This is particularly the case with image intensifiers of the microchannel plate electron multiplier type, due to the variation in physical properties from intensifier to intensifier of the materials used in the microchannel plate construction and the change in electrical characteristics thereof with changing ambient temperature and changing input power supply voltage. Accordingly, such image intensifiers require a controlled variation in input voltage thereto with changing ambient temperature and a regulated power supply voltage to prevent decreasing intensifier lightness with decreasing input voltage, as could occur with extended use with a battery. Additionally, the response to light variation of intensifiers used in pairs, such as in night-vision goggles, has heretofore required separate power supplies, one supply for each image intensifier, due to the foregoing and due to the prior art power supply systems, which sense current on the high voltage side of the power supply, in the nanoamp range rather than on the low voltage side of the supply, in the milliamp range as in the present invention. Further, prior art systems not based upon total tube current control could not distinguish between tubes, hence could control only a single tube. In contrast, the present system provides a single supply, with separate ac to dc converters and voltage multipliers for each intensifier tube. Thus, while prior art systems attempted to detect screen currents in the nanoamp range, with their attendant leakage and crosstalk problems, the present invention detects total current level of two or more intensifier tubes. By detecting the effective change in power demand by each intensifier tube with changing light level, and limiting the power supplied to the tubes, a simplified power supply is provided. It has been heretofore unexpected that there would be sufficient change in current demand with increasing light level to control the output light level. Furthermore, it had been heretofore unexpected that by utilizing constant current control on the primary side of the power supply, and in a multi-tube system, that the high light level saturation characteristics would be relatively constant over a wide range, i.e. approximately five decades of tube input light illumination in ft. candles, and that the changes in operating power of one tube could be distinguished from another.